The present invention relates to a shutoff device for a fluid. Particularly, the present invention relates to a device of the type comprising a body having a conduit in which, in use, a fluid is adapted to flow, a plunger sliding in a seat formed in said body and provided with an end portion suited to shut off said conduit, and means controlling the movement of the plunger into the seat between a first and a second working positions in which the above-mentioned end portion shuts and opens the conduit respectively.
Shutoff devices of the above specified type are differently used for various purposes: for instance, they are used as servovalves of the proportional or on-off type, or as injectors of a fuel in the field of the endothermic engines. In particular, in order to increase the efficiency of the engines, especially of the diesel type engines, different solutions have been studied relating to the injection, especially in connection with the increase of the injection pressure, the reduction of the injection time and, in general, the improving of the control in every stage. In this connection, studies are known in which it is provided the use of control means for the movement of the plunger: in particular, it is known an embodiment of an injector which makes use as actuator for the movement of the plunger of a member made in piezoelectric material and having the shape of a cylinder. Such an actuator is known only on an experimental basis and presents certain drawbacks that have not allowed the production on an industrial scale. As a matter of fact, the piezoelectric cylinder presents the risk of depolarization in the event that in operation be exceeded a critical pressure level; further, said cylinder has a coefficient of cubical expansion rather low and in use must be enclosed inside a cylindric expansible container.